A NETWORK SIMULATION FOR DRAINAGE OF STATIC FOAM COLUMNS

A simple cylindrical network consisting of regular hexagons is used to simulate the flow during drainage in a static foam column. The dimensions of the network are calculated by considering the foam to consist of regular pentagonal dodecahedral bubbles. Simulations offer several new insights concerning the microscopic origin of the nonlinearity and inflection in the drainage plot. It is shown that the contraction of Plateau border channels in the presence of bubbles of varying sizes causes the observed nonlinearity in the drainage plot. Inflection in the drainage plot can be observed only when the liquid volume fraction increases with column height. Other calculations concerning the effects of bubble size and column height are consistent with experimental observations

A review on experimental studies of surfactant adsorption at the hydrophilic solid–water interface

The progresses of understanding of the surfactant adsorption at the hydrophilic solid–liquid interface from extensive experimental studies are reviewed here. In this respect the kinetic and equilibrium studies involves anionic, cationic, non-ionic and mixed surfactants at the solid surface from the solution. Kinetics and equilibrium adsorption of surfactants at the solid–liquid interface depend on the nature of surfactants and the nature of the solid surface. Studies have been reported on adsorption kinetics at the solid–liquid interface primarily on the adsorption of non-ionic surfactant on silica and limited studies on cationic surfactant on silica and anionic surfactant on cotton and cellulose. The typical isotherm of surfactants in general, can be subdivided into four regions. Four-regime isotherm was mainly observed for adsorption of ionic surfactant on oppositely charged solid surface and adsorption of non-ionic surfactant on silica surface. Region IV of the adsorption isotherm is commonly a plateau region above the CMC, it may also show a maximum above the CMC. Isotherms of four different regions are discussed in detail. Influences of different parameters such as molecular structure, temperature, salt concentration that are very important in surfactant adsorption are reviewed here. Atomic force microscopy study of different surfactants show the self-assembly and mechanism of adsorption at the solid–liquid interface. Adsorption behaviour and mechanism of different mixed surfactant systems such as anionic–cationic, anionic–non-ionic and cationic–non-ionic are reviewed. Mixture of surface-active materials can show synergistic interactions, which can be manifested as enhanced surface activity, spreading, foaming, detergency and many other phenomena.© Elsevie

Effects of the intermicellar exchange rate and cations on the size of silver chloride nanoparticles formed in reverse micelles of AOT

Nanoparticles of silver chloride have been synthesized by the method of mixing of two microemulsions, one containing silver ions and other containing chloride ions. The effects of changing the intermicellar exchange rate by varying the continuous phase, by adding benzyl alcohol, and by varying the water to surfactant molar ratio as well as the effect of cations (metal chlorides from the first and second group of the periodic table) on the particle size and the size distribution and the number density have been studied. The particle diameters are measured from the photomicrographs obtained by transmission electron microscopy. The average particle size, the polydispersity, and the number of particles formed are shown to be dependent on the intermicellar exchange rate and/or the rigidity of the surfactant shell. This dependency can be qualitatively explained by means of nucleation and growth phenomena, as mediated by the intermicellar exchange of contents

Effects of intermicellar exchange rate on the formation of silver nanoparticles in reverse microemulsions of AOT

We report the effects of intermicellar exchange rate on absorption spectra and particle size of silver nanoparticles synthesized in reverse micelles of AOT. The silver nanoparticles are prepared by the method of mixing of two microemulsions, one containing the silver nitrate and the other containing sodium borohydride. The intermicellar exchange rate is varied by changing the organic solvent, surfactant (SDS, NP-5, and DTAB), and organic (benzyl alcohol and toluene) additives. The higher intermicellar exchange rate is found to give smaller particle size and blue shift in the absorption spectra. An interesting and potentially useful effect has been observed in that addition of a small amount of a nonionic surfactant significantly reduces the particle size

STABILITY OF AQUEOUS FOAMS WITH POLYMER ADDITIVES .3. MEASUREMENTS AND CALCULATIONS OF STABILITY OF FOAMS GENERATED AT DIFFERENT PRESSURES

The stability of aqueous foams with polymer additives has been studied at different generation pressures. While the stability increases significantly with the increase of generation pressure for foams without any additive, it, however, changes weakly with the change in generation pressure for foams with polymer additives. Consistent with the previously reported studies, it is found that the foam stability (drainage half-life) increases, primarily due to the decrease of bubble size, at higher generation pressures, when the foam is produced in a packed bed. Calculations of drainage half-life were conducted using a modified lamella drainage model as well as a simple network model. It is found that the network model predictions agree reasonably well with measurements. (C) 1994